Technological advances in computer networks not only improve textual information exchange but also open a new avenue for voice communication. Traditional telephone communication networks are no longer sole providers of quality voice data services. As networking technologies improve, an emerging Voice over Internet Protocol (VoIP) becomes a cost-effective alternative to make a phone call, compared to landline and mobile phone call. A VoIP call is typically initiated by or terminated to a VoIP device, such as a personal computer (PC), Wi-Fi phone, or session initiation protocol (SIP) Phone.
Currently, a VoIP call directed to or terminated at a regular landline or mobile phone is normally paid by a caller (i.e., a calling party). If the callee (i.e., called party) is a merchant who is willing to pay for the VoIP call, the so-called Merchant Powered Click-to-Call (MPC) allows a caller to call a merchant for free. This normally happens at search web sites. A significant usability disadvantage in this mechanism is that it requires a special mapping from a code name to a real phone number in the backend server; as a result, the user won't directly know the real phone number. Moreover, the user must always make a call from the same web site to enjoy a free call (or receive pre-authorized credit for the call).